Problems of measuring mechanical quantities in technical objects occur rather often. This happens both at the stage of various machines design, mechanisms, structures, vehicles etc., and in their operation. Very often these problems are solved by applying the methods and means of strain gauging, where the main measuring device is a resistant strain gauge.
The main disadvantages of existent resistant strain gauges are their low gauge factor, the dependence of the output signal from the temperature which is characterized by the temperature coefficient of resistance that leads to a decrease in accuracy. The gauge factor K is defined as the ratio of the relative change in electrical resistance of resistant strain gauge ΔR/R to the value of relative deformation ∈, K=(ΔR/R)/∈. Temperature coefficient of resistance α (TCR) is defined as the relative change in electrical resistance of resistant strain gauge at temperature change by one degree, α=(ΔR/R)/ΔT.
A resistant strain gauge for measurement of deformations and pressure in which the strain-sensing element is executed on the basis of a thin polycrystalline film of samarium sulfide—the SmS is known (V. V. Kaminskii, I. A. Smirnov Rare-earth semiconductors in mechanical quantities' sensors. Devices and control systems 1985, Vol. 8, pp. 22-24). It has high gauge factor and good linearity of the output characteristics in the climatic temperature range. Its construction represents a dielectric substrate on which the strain-sensing layer from SmS and metal contact pads are placed and to which output wires are soldered. If the substrate deforms the SmS layer also deforms, having an electrical resistance in direct proportion to the deformation. This change in electrical resistance is fixed by electronic equipment.
The main disadvantage of this resistant strain gauge is a significant change in the relative electrical resistance ΔR/R under the influence of temperature, so that the temperature coefficient of resistance α in the climatic temperature range varies from (−2×10−3 deg−1) to (−4×10−3 deg−1), which leads to an increase in measurement error.
A resistant strain gauge for measurement of deformations and pressure on the basis of a polycrystalline SmS thin film (author's certificate SU no. 1717946, G01B7/16, G01B7/18), which is placed on a dielectric substrate, is taken as a prototype of the suggested resistant strain gauge and its versions. Metal contact pads with soldered output wires are connected to the film. The resistant strain gauge has a high gauge factor K=40; temperature coefficient of resistance (TCR) is α=−2×10−3 deg−1.
Its disadvantage is a large value of temperature coefficient of resistance (TCR), which leads to measurement errors and reduced accuracy.